Tomble

Damn, sorry, I've been busy with my own "computer ports" problem (*shudder*) for the past week or so, so I've not been on the site.

A very quick answer whilst I have time:
-You only need to get RS232 voltage levels if you're interfacing with a SERIAL port. DO NOT use a MAX232 or similar to interface with a parallel port!!!! I don't know whether they'd go "bang" or not but regardless, it isn't correct. Parallel ports work with normal 0-5V levels.
-You normally only need a buffer in the computer if you're receiving data that is in some way serial.
-In the case of receiving data through the serial ports themselves in the standard serial port transmission method, there are buffers already in the port, you just set the right speed etc, and read what the operating system gives you. You don't "create" a buffer!
-In the case of reading individual pins of the serial port directly, you bypass the buffer, but you won't be doing this in your case. That's for weird applications.
-In the case of the parallel port, AFAIK there is no buffer built into the port, but USUALLY you don't need one. If you're sending data 4 bits at a time (out of 8 or 10 bits per word to be sent), you would need some software buffer in your receiver program, to reassemble the sample data. This could get messy.
-If you're transmitting the sample data through the parallel port 8 or so bits at a time, you don't need a buffer, you just need to do whatever you want to do with the data, like send it to a file or something. I'm not sure what you're doing with it.

IMPORTANT BIT:
If you're sending the data serially (either 1 bit at a time through the serial port, OR 4 bits at a time over the parallel port), then you most likely need to use a microcontroller, else the hardware will get pretty complicated. The pro side of this is that many microcontrollers have built in ADC, so less components for that. The con of it is that you'd need to be able to program the thing.

If you're not going to do that then you should do as various people had suggested and use a separate ADC chip and send it through the parallel port. Presumably this requires setting the parallel port to be ECP or EPP or bidirectional or whatever the thing is, to be able to send more than 4 bits back to the PC, because AFAIK the "standard printer port" type arrangement doesn't allow for that. I expect someone else can explain that bit.

Now, can someone else fill in the blanks on that? Because I'm not sufficiently knowledgeable about parallel ports, and am rather tied up with this networking crap I have to work on.

helz15

Oh I am really getting myself confused, I underestimated how hard this was going to be.

Ok, so I need to decide if I am using the serial or parallel port before I start making things go bang!

So if I was to go down the rout of the serial port, then I will need a chip that has an A/D converter and makes the RS232 voltage levels.

Now I don’t know anything about programming microcontrollers, but this is a college project, so I will find out what microcontrollers the college have the facilities to program (as I am assuming you need equipment to do this?)

So then, the basic stages involved in my project will be:
Set up the circuit as shown in the diagram (attached to a previous post)
Replace the AVO with a resistor (don't know what size) to get a voltage reading.
Find a chip that makes it RS232
Use a microcontroller (with A/D converter)
plug into Serial port

Then I am hoping I will be able to see the voltage reading in a computer program such as Visual basic (or any other easily available computer program).


Thanks for being so patient with me!

Tomble

Well, I may have made things SOUND more confusing than they need to be. If so, sorry

Well yes, each port is dealt with pretty differently in numerous ways.

IF you go down that route, then you'd have to have those things, but they wouldn't have to be in the same chip. You'd probably have a microcontroller with the A/D converter, and that'd send out serial data at "TTL logic levels" (0-5V), and then feed that to a MAX232 type chip to get the RS232 voltages. But that remains an "if". Other people's suggestion of using the parallel port would probably be better, depending on what you can do.

The hardware for programming PIC microcontrollers, if you use those, can be relatively simple. But you also need various pieces of programming software, and to know a language you can effectively program the chip with. So if you don't have ANY experience with microcontrollers, then you might get terribly bogged down with all this, which would be a very good reason to use the parallel port approach instead, if you can. OR maybe that gameport approach might be workable somehow?

If you were using the serial port approach, it would be VAGUELY like that, but it looks somewhat out of order. Gimme a little while and I'll knock out a simple diagram (not schematic, sorry). It might clarify things.

Meanwhile, as this is cropping up and I keep forgetting to ask: Can you program, and if so, in which languages?

helz15

As far as programming is concerned, technically, no I cannot program, however, my brother is a computer programmer and is willing to ‘help’ me with that bit, he can program in Java, PL/SQL, Ruby, PHP, C#, and a bit in VB.

I am happy to change to using the parallel port if you think that would be easier for me, I really am happy to go down the route you think is best/easiest.

blueroomelectronics

There are a few multimeters with built in RS232. Why not just use one.

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com

Tomble

Ok, as I'd gone and made things overly confusing, here's that diagram. It doesn't include the software on the PCs I'm afraid. serial-vs-parallel.pdf

FWIW if it's not clear, it's probably best to go for the parallel port method, if there's something that can read it effectively. Or else perhaps some sort of commercial "signal logger" type device, which might come with its own software? I don't know. I most probably shouldn't have even mentioned the serial port approach in the first place, that's just what usually seems easiest to me, but you're not me! The parallel port has its issues but they might not be a problem for you.

It's also probably a very good idea to ask your teachers what they'd recommend, as they'd probably have a better idea what you'd be able to deal with and what your computers could use. Your college might even already have a signal logger like I described!!

(Oh, or Bill's idea there might be good, if your college has one of those; I'd imagine they're expensive to buy yourself?)

helz15

Ok, thanks very much for your help!
That diagram helps alot!!!!

I am at college tomorrow, so i will ask some questions and get back to you.

Thanks again!

Overclocked

How about a DataQ Data logger?
http://www.dataq.com/products/startkit/di194rs.htm

nater

please helppppp me for about for major project in electrical duscipline.

Tomble

First: Nater, please start a new thread of your own to ask for help. Go to one of the forum pages here, such as http://www.electro-tech-online.com/g...ctronics-chat/, and click the button that says "New Thread". When you start your new thread, please be sure to explain what your problem actually is too

Second: Helz15, if you're still reading, I dunno if you got anywhere with asking your teachers for advice, but I must say that Overclocked's suggestion of that data logger is a very good one. I couldn't remember the proper term before, but from what little I've seen of such things in the past, that one is a really good price (about £12?). It would probably save you a ton of bother, if the college doesn't already have some equivalent for you to use No need to worry about building your own PC interface that way.